Near-Optimal Quantum Algorithms for String Problems

10/19/2021
by   Shyan Akmal, et al.
0

We study quantum algorithms for several fundamental string problems, including Longest Common Substring, Lexicographically Minimal String Rotation, and Longest Square Substring. These problems have been widely studied in the stringology literature since the 1970s, and are known to be solvable by near-linear time classical algorithms. In this work, we give quantum algorithms for these problems with near-optimal query complexities and time complexities. Specifically, we show that: - Longest Common Substring can be solved by a quantum algorithm in Õ(n^2/3) time, improving upon the recent Õ(n^5/6)-time algorithm by Le Gall and Seddighin (2020). Our algorithm uses the MNRS quantum walk framework, together with a careful combination of string synchronizing sets (Kempa and Kociumaka, 2019) and generalized difference covers. - Lexicographically Minimal String Rotation can be solved by a quantum algorithm in n^1/2 + o(1) time, improving upon the recent Õ(n^3/4)-time algorithm by Wang and Ying (2020). We design our algorithm by first giving a new classical divide-and-conquer algorithm in near-linear time based on exclusion rules, and then speeding it up quadratically using nested Grover search and quantum minimum finding. - Longest Square Substring can be solved by a quantum algorithm in Õ(√(n)) time. Our algorithm is an adaptation of the algorithm by Le Gall and Seddighin (2020) for the Longest Palindromic Substring problem, but uses additional techniques to overcome the difficulty that binary search no longer applies. Our techniques naturally extend to other related string problems, such as Longest Repeated Substring, Longest Lyndon Substring, and Minimal Suffix.

READ FULL TEXT

page 1

page 2

page 3

page 4

research
10/23/2020

Quantum Meets Fine-grained Complexity: Sublinear Time Quantum Algorithms for String Problems

Longest common substring (LCS), longest palindrome substring (LPS), and ...
research
10/12/2022

Quantum divide and conquer

The divide-and-conquer framework, used extensively in classical algorith...
research
09/03/2023

Longest Common Substring and Longest Palindromic Substring in 𝒪̃(√(n)) Time

The Longest Common Substring (LCS) and Longest Palindromic Substring (LP...
research
10/17/2022

A Note on Quantum Divide and Conquer for Minimal String Rotation

Lexicographically minimal string rotation is a fundamental problem on st...
research
03/15/2019

Smallest k-Enclosing Rectangle Revisited

Given a set of n points in the plane, and a parameter k, we consider the...
research
08/02/2018

Improved Quantum Information Set Decoding

In this paper we present quantum information set decoding (ISD) algorith...
research
04/19/2020

Quantum algorithms for computational geometry problems

We study quantum algorithms for problems in computational geometry, such...

Please sign up or login with your details

Forgot password? Click here to reset